Vegetation trimming devices are well known and are commonly used to maintain one's lawn and garden. There are a number of different classifications of rotary trimmer heads, defined generally by the manner in which a monofilament trimmer line is fed, spooled or replaced in the trimmer head and/or how the trimmer line is discharged, indexed or lengthened during use of the trimmer head. Such classifications include (a) “self-indexing” trimmer heads, wherein trimmer line is automatically released from a spool inside the trimmer head upon a determination of increased rotational speed of the trimmer head, (b) “bump-fed” or “bump-activated” trimmer heads, wherein trimmer line is mechanically released from a spool inside the trimmer head by the user “bumping” the bump knob or similar member on the ground so as to permit a length of line to be released, and (c) “fixed-line” trimmer heads, wherein a length of line is introduced and inserted manually through spaced openings at the periphery of the trimmer head into a line-holding mechanism that holds the trimmer line to the trimmer head during use, eliminating the need for a spool.
The majority of aftermarket trimmer heads sold are (c) “fixed-line” trimmer heads because they are easily designed to be universally adaptable to essentially any brand of rotary trimmer regardless of the operation of the trimmer head or the direction of rotation. Replacement strips of trimmer line used for this type of trimmer head are typically about 8 to 15 inch in length and can be easily added to the head through the openings. More particularly, fixed-line heads use a base portion having a series of radially spaced line holders, each capable of holding one strip of trimmer line. After the line strip wears, the consumer manually removes the used strip, either through the openings, if possible, or more likely, through a discharge port located near the radial center of and on the top or bottom of the trimmer head. Once the old worn length of line is removed, a new length of trimmer line can be inserted into the line holding mechanism. There is no indexing or lengthening of the line during use. The ease-of-use has been a reason for the market acceptance of this type trimmer head. However, the need for improvement still exists for this type of trimmer head.
There are a variety of methods and mechanisms developed and discussed in the prior art for holding a fixed length of trimmer line to a trimmer head. Among the more popular methods for holding strips of line include (i) means for holding one end of a strip of line such that one end is held by the trimmer head, while the other end impacts and cuts vegetation, (ii) means for holding a folded strip of line such that one and typically both ends of the strip of line impacts or cuts vegetation, or (iii) means for holding the strip of line in the middle such that both distal ends extend from the trimmer head for impacting and cutting vegetation. Since the present invention is focused on improving fixed-line trimmer heads that hold only one end of each line strip, the prior art and problems associated with these line-holding mechanisms are further discussed.
U.S. Pat. Nos. 5,758,424 and 5,896,666 describe the use of a single biased pivoting cam adjacent to a pressing wall, whereby the trimmer line is pinched between the cam and the pressing wall. With these clamping concepts, line can be inserted and removed when the line moves in one direction, but the line cannot move in the opposite direction.
Similarly, U.S. Pat. No. 6,581,292 teaches the use of a sliding cleat. The cleat is bias to a first position as to cause the cleat to touch the far wall of a line channel. A strip of trimmer line can be inserted into the line channel, which causes the cleat to move to a second position and allows a portion of the line to pass into the line channel and partially past the cleat. The line can be inserted and moved in one direction, but cannot be removed if pulled in the opposite direction, unless pulled with significant force.
Another means of holding a fixed length of line is taught by U.S. Pat. No. 6,347,455. In this patent, pairs of cams are used to grip the line. In the '455 patent, the cams are not biased, but operatively connected to an actuator. The actuator is biased. Each actuator is biased such that a pair of cams are forced together to form a pinch point. A fixed length of trimmer line can be inserted between the two cams in one direction, but cannot be removed if pulled in the opposite direction.
While not discussed in some of these patents, the early commercialized fixed-line trimmer heads based upon the above discussed clamping means for holding trimmer line all had one thing in common. These heads all had a lower central cavity defined within the housing of the trimmer head that was open to the lower side of the trimmer head and a straight line channel that extended from an opening on the outer perimeter of the trimmer head to an opposite opening located on the inside perimeter of the trimmer head defined by this lower central cavity. The line channels were all straight and positioned essentially radially and perpendicular to the axis of rotation. This configuration allowed the user to insert the line from the outside perimeter of the head. One distal end of the line would be left extending from the trimmer head for the purpose of contacting and cutting the vegetation upon rotation of the head, while the other distal end of the line would extend past the clamp and into this lower central cavity. This allowed the user to later grab the end extending into the lower central cavity for the purpose of removing the line when the time arose to install a new strip of line into the trimmer head.
A common problem with the line channel configurations discussed above is that dirt and debris would enter the line channel(s) from the opening(s) along the lower central cavity and would travel along the line channel(s) towards the outer opening(s) located on the perimeter of the trimmer head. This would occur even with line installed in the line channel. Without being bound to theory, it is believed this problem is caused due to the construction of the trimmer head wherein a vacuum is created during the high speed rotation of the trimmer head such that dirt and debris are sucked into the trimmer head openings, particularly the openings in the trimmer head long the lower central cavity.
It has been found that this dirt and debris traveling along the line channel to the inside of the head would often collect around the clamp and eventually would interfere with the movement of the pivoting or reciprocating clamps. Such debris can cause the clamping means to stop functioning. This problem has been the source of much frustration among users of this type of fixed-line trimmer head.
After extended use, the commercial trimmer heads of the types taught in U.S. Pat. Nos. 5,758,424, 5,896,666 and 6,581,292 will sometimes fail by not releasing the line or by no longer gripping the line. This generally happens due to the clamp becoming stuck due to debris which has collected inside the trimmer head. The trimmer heads taught by U.S. Pat. No. 6,347,455 are unique in that an actuator could be used to open the pinch point between the dual-facing clamps. However, eventually enough debris can collect in trimmer heads of even this design and prevent the actuator from being able to move the clamps.
Attempts have been made to counter this problem. In U.S. Patent Application Publication Nos. US 2008/0271424 and US 2008/0083120, the line channel extends from the outer perimeter of the head to a point located on the upper surface of the trimmer head, as opposed to the lower central cavity of the other line channel designs. However, upon analysis of trimmer heads having this line channel configuration, it has been determined that simply locating the second opening for the line outlet on the upper surface of the head does not solve the problem of dirt and debris being pulled into the head. And, these two later approaches do not provide a means such as an actuator to open the pinch point as was taught by U.S. Pat. No. 6,347,455.
Thus, the need exists for an improved fixed-line trimmer head of the type capable of holding at least one strip of line such that one end of the strip of line is held by the trimmer head, while the other end impacts and cuts vegetation. Such a trimmer head should have a line-holding mechanism that can be loaded from the perimeter of the head and discharged from another position on the head and yet will not allow any significant amount of debris and dirt to be drawn into the head.
Another challenge with any fixed-line trimmer head is gripping the line sufficiently tight enough so that the line is not pulled from the head when impacting objects like fences, posts and rocks, and yet capable of releasing the line when the times comes to replace the line. Keeping dirt and debris out of the head is important if the head is to continue to function by allowing the clamps to grip and release the line.